During steady state conditions, airflow into an intake manifold of an engine via a throttle and EGR may be allocated to deliver a desired cylinder airflow amount while maintaining desired EGR in the cylinder. However, during transient conditions, the intake manifold acts as an air buffer and thus the airflow reaching the cylinder may lead or lag desired airflow amounts entering into the manifold. This may result in poor torque response and/or transient EGR disturbances.
U.S. Pat. No. 5,273,019 describes a model for predicting mass air flow into an engine, both with and without EGR, during the same transient condition event. Based on a difference between the models, the percentage of the mass flow that derives from EGR may be determined. While the disclosed models enable determination of EGR concentration during transient events, they do not provide for maintaining a desired cylinder EGR amount, nor do they overcome the delay often associated with achieving a desired cylinder airflow amount during a transient event.
The inventors have recognized the issues with the above approach and offer a method to at least partly address them. In one embodiment, a method for controlling airflow into a cylinder of an engine comprises, if a previous cylinder airflow is different than a desired cylinder airflow, allocating flow into an intake manifold between a throttle and an EGR valve to provide the desired cylinder airflow while maintaining a desired EGR amount in the cylinder.
In this way, both the throttle and EGR valve may be controlled using transient airflow compensation to achieve rapid filling or unfilling of an intake manifold. Further, by allocating the flow between the throttle and the EGR valve, a desired EGR amount in the cylinder may be maintained. In one example, the desired cylinder airflow may be a prediction based on the previous cylinder airflow, a manifold filling model, and a driver torque request. The manifold filling model may determine a compensation airflow amount entering the manifold that rapidly drives the airflow leaving the manifold from the previous cylinder airflow amount to the desired cylinder airflow amount. This compensation airflow amount may be allocated between the throttle and the EGR valve to provide the desired cylinder airflow while maintaining a desired cylinder EGR amount.
The present disclosure may provide several advantages. First, transient conditions frequently result in torque fluctuations that can be unsatisfactory to a vehicle operator. By rapidly responding to a requested torque change, the present disclosure may improve vehicle response and operator satisfaction. Further, EGR disturbances during transient conditions may degrade combustion events, leading to reduced fuel economy and increased emissions. By maintaining desired EGR amounts even during transient events, fuel economy and emissions may be improved.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.